Many types and mixtures of metal salts and soaps of natural or synthetic organic acids, particularly carboxylic acids, have been suggested and commercially offered over several decades. These have been used to supply metals in forms which are soluble in organic liquids, particularly in various hydrocarbon oils and solvents, to form solutions having various desired properties and uses. For example, such metal salts have found uses as catalysts and as fuel and lubricant additives. Metal salts of carboxylic acids also are useful as stabilizers for various polymers including polyvinyl chloride-type plastics, and in the area of drying catalysts for paints, varnishes and other coating compositions.
However, since gold is the most noble of the noble metals, gold is not dissolved by most acids under ordinary conditions. Gold complexes, such as chloroauric acid formed by the reaction of gold with aqua regia (3:1 hydrochloric:nitric acid), and alkali (dicyano)gold(I) formed by a reaction between gold and an alkaline cyanide solution in the presence of air or hydrogen peroxide, are compounds generally bound more strongly to the respective anions than the ligands produced between gold and carboxylates, making it difficult to separate gold carboxylates from a solution containing these other ligands. These other ligands are considered undesirable in a number of applications in which gold carboxylates would be desired.
For example, the catalytic and co-catalytic properties of gold may be inhibited by the presence of chloride ions or chlorine-containing compounds, such as when gold is used as a catalyst for the production of phenol acetate. Nitrogen compounds such as amines, amides and cyanides; phosphorus compounds such as phosphate, phosphine complex compounds; and sulfur compounds such as sulfates, sulfones, sulfoxides and sulfides may also act as a catalyst poison. The cyanides, of course, are also undesirable from a human toxicological viewpoint.
U.S. Pat. No. 3,687,993 to Hornig, deceased, et al describes a process for making solid gold hydroxy diacetate of the formula Au(OH)(O.sub.2 CCH.sub.3).sub.2 and its use as a catalyst or catalyst component for homogeneous or heterogeneous reactions. It is also mentioned that the gold hydroxy diacetate may be used for manufacture of other organic gold compounds such as reacting it with propionic acid, or with other carboxylic acids, to yield a corresponding gold compound.
Takiguchi et al, "Synthesis of naphthenates of gold, silver, platinum and palladium and bisoxime palladium dichlorides," Kagyo Kagaku Zasshi, Vol. 72, No.7, (Japan 1969) pp. 1549-1551, describes reactions of chloroauric acid and chloroplatinic acid with sodium naphthenate, and reports that the direct reaction between an aqueous solution of chloroauric acid and sodium naphthenate lacked reproducibility and yield and the direct reactions between chloroplatinic acid and sodium naphthenate caused marked precipitation of metal and "did not produce a good result."
U.S. Pat. No. 3,700,458 (Lindholm) describes a chemical process for preparing noble metal salts of carboxylic acids useful in photosensitive and thermosensitive compositions. The process involves mixing a non-aqueous solution of an organic carboxylic acid with a non-aqueous solution of a noble metal trifluoroacetate or tetrafluoroborate in the presence of an organic peptizer. A variety of organic peptizers are disclosed including polyvinyl acetals and certain acrylate copolymers.
As far as the inventor is aware, none of the foregoing processes provides a facile means for obtaining gold carboxylates, particularly gold carboxylates derived from carboxylic acids having a molecular weight higher than acetic acid.